The present invention relates to a coordinate measuring machine and method for determining spatial coordinates on a measurement object.
EP 1 071 922 B1 discloses a prior art coordinate measuring machine and a corresponding method. The known coordinate measuring machine has a probe element, which is arranged at the end of an elastically flexible optical fiber. The probe element serves to touch a measurement point on a measurement object. By using an optical sensor, which includes a camera and a lens assembly, it is possible to detect deflections of the probe element when probing the measurement object. On the basis of the deflection of the probe element and on the basis of the position of the optical sensor relative to the measurement object, if desired, it is then possible to determine spatial coordinates for the probed measurement point. Alternatively, the known coordinate measuring machine is supposed to offer the option of measuring the surface topography of a measurement object without using the probe element, i.e. in a purely optical fashion. EP 1 071 922 B1 proposes that the optical sensor comprises a zoom optics with two lens-element groups, which, with the aid of motors, are moved separately into positions for magnification and distance from the measurement object. This is supposed to make it possible to remove the probe element from the depth-of-field range of the optical unit in order to enable a purely optical measurement, if desired.
JP 2011-169661 discloses an optical measuring machine with a camera and a telecentric optical system that comprises a front lens element, a rear lens element and a telecentric stop. The measuring machine further comprises a laser-based autofocus system, which determines a position of the measurement object on the optical axis of the telecentric system with the aid of laser light.
The use of optical sensors in conjunction with coordinate measuring machines makes it possible, in many cases, to measure geometric properties of a measurement object very quickly. A disadvantage of known coordinate measuring machines with optical systems until now lies in the fact that the optical sensors are restricted to specific measurement tasks and specific workpiece properties. The optical sensors are generally optimized for a specific type of measurement object, for example in respect of the achievable measurement accuracy or the measurement region. By way of example, workpieces that have great height differences in the direction of the optical axis of the sensor may cause problems. In part, use is made of different optical and/or tactile sensors in order to be able to flexibly react to different measurement requirements, wherein the individual sensors each only assume part of the overall measurement object. In general, each individual sensor is optimized for a specific measurement object. Particularly, optical sensors therefore comprise an individual optical system that is well-suited to one specific purpose but less well-suited to other purposes.
Providing different sensors for various measurement objects in a coordinate measuring machine enables high flexibility in conjunction with high measurement accuracy. Disadvantages include the high costs for providing the plurality of sensors, each having optics adapted to the specific purpose. Moreover, the plurality of sensors, each with individual optics, require a relatively large installation space in the coordinate measuring machine, which restricts the measurement volume and incurs further costs.